1. Field of the Invention
This invention relates to drug delivery techniques, and more particularly relates to such techniques for treating neurodegenerative disorders.
2. Description of Related Art
There are a number of conventional apparatuses and methods for drug delivery to a patient. Implanted drug delivery systems have involved two general approaches. One approach is to use an implanted drug administration device, wherein drugs are pumped from a reservoir to a target site within a patient. See e.g., U.S. Pat. Nos. 5,711,316; 4,692,147; 5,462,525; and 4,003,379. The reservoir can be replenished as necessary through a replenishing port, and without removal of the implanted device from the patient. Some drugs are not stable when dissolved in a vehicle delivery solvent. Other drugs are stable for only a short period of time when dissolved in a solvent. Some drugs are stable for example for only 30 to 90 days. After that time, the drug will precipitate out of solution, or the drug molecule may be altered. When a significant amount of the drug has degraded, the solution has to replaced, even if a useful quantity is still available in the reservoir. When this occurs, the patient must visit a medical center to have the reservoir emptied of the degraded solution and refilled with non-degraded solution.
Most conventional devices store the drug to be delivered in a reservoir, with the drug dissolved in a liquid solvent, such as water or saline. The stored solution is quite dilute, e.g. 1-5% of the drug compared to 95-99% carrier. Further, the reservoir in the device for the delivered drug must be large enough for the requisite solvent, and the reservoir must be replenished frequently. Thus, there is a need for devices and methods that can deliver drugs that are not stable when dissolved in a solvent, and to do so in a controlled manner. There is also a need for smaller devices that do not have the large reservoir required by conventional devices and methods.
A second approach has been to use implanted capsules that will permit the drug within the capsule to transfer outside of the capsule wall by diffusion and/or by the dissolving of the capsule wall. See e.g., U.S. Pat. Nos. 5,106,627 and 5,639,275. A major drawback with this approach is that it is a passive drug delivery system that drug delivery cannot be controlled after implantation of the capsule within the patient. Further, additional capsules must be implanted after earlier capsules are dissolved or spent.
In addition, conventional sensing systems are limited due to the fact that certain substances are not directly measurable using conventional sensors. In these circumstances, the substance must be reacted with a reagent to produce a substance that can be directly measured using conventional sensors. As an example, oxygen can but glucose cannot be directly measured by conventional sensors, so an oxidase is reacted with glucose to produce oxygen, the level of which is then directly measured by the sensor and which corresponds to the level of glucose at the target site. A conventional manner for providing reagent to produce a measurable substance is one that has a set amount of initial reagent within a disposable sensor. A drawback of this conventional approach is that the reagent is consumed and there is no way to replenish the consumed reagent short of removing the disposable sensor and replacing it with a new disposable sensor containing reagent. Alternative methods for providing a sufficient amount of reagent to produce the directly measurable substance are desirable, particularly to extend the useful life of a sensor.
The present invention is directed to these difficulties which the prior art fails to address.
A preferred form of the invention can provide controlled drug delivery. The drug is stored within an implantable device in solid form. Small amounts of the drug, e.g. 1 microgram, are encapsulated in an inert material, e.g. a stable polymer. The encapsulated drug is stored in a reservoir of the implantable device. Further, there may be a supply of pure carrier in the implantable infusion device. This can be a separate carrier, such as water, stored in a separate reservoir system. In addition, the supply of pure carrier can be replenished.
The carrier can also be a body fluid, such as cerebrospinal fluid from the patient""s body. This concept of dissolving a drug into a stream of recirculating body fluid is disclosed in U.S. Pat. No. 5,643,207, which is incorporated herein by reference.
When drug infusion is desired, some of the encapsulated drug is metered by the implantable device into the carrier fluid. The capsules are broken, thereby freeing the drug to be dissolved in the carrier fluid within the device. The carrier fluid with the dissolved drug is then infused by an electromechanical pump of the device to the target site within the patient.
The capsules can be broken in any suitable manner by a drug releaser involving any suitable mechanism, including: ultrasonic waves, mechanical crushing or grinding; chemically dissolving or splitting; applying an electrical current to potentiate a chemical reaction; heating; or applying pressure (e.g. hydrostatic pressure). Thus, in accordance with the present invention, the drug releaser can comprise, by way of example, an ultrasonic sound emitter, a mechanical crushing or grinding device, a chemical dissolving or chemical splitting apparatus, an electrical current emitter, a heater, or a pressure device.
It is an objective of the present invention to provide implantable devices and methods for drug delivery that are smaller than conventional devices and methods.
It is a further objective of the present invention to provide implantable devices and methods for drug delivery for longer periods of time without replenishing than is required for conventional devices and methods.
It is a further objective of the present invention to provide implantable devices and methods for delivery of drugs that are not stable when dissolved in a fluid.
It is a further objective of the present invention to provide alternative methods to replenish reagents required for chemical reactions to produce substances that can be directly measured using conventional sensors, as well as to extend sensor life.
Those of skill in the art will recognize these and other benefits that the above apparatus and methods provide over conventional devices.